The overall objective of the proposed research is to define the mechanism of alkylation of cellular targets such as nucleophilic sites in DNA and RNA, by carcinogenic nitrosamines. In addition to direct transfer of intact alkyl groups to cellular nucleic acids, methylation appears to be a reaction common to several dialkylnitrosamines and possibly cyclic nitrosamines. Using N-nitrosodipropylamine and N-nitrosopiperidine as examples of the two classes of nitrosamines, the mechanism of formation of methylating agents by these compounds and their beta-oxidized derivatives in isolated rat liver preparations will be investigated.